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Background

MicroRNAs (miRs), a class of small non-coding RNA molecules, act as posttranscriptional
regulators and are involved in a plethora of cellular functions. miRs have attracted
a great deal of attention as potential therapeutic targets, as the sequence-specific
mode in which they act, allows the simultaneous targeting of multiple target genes,
often members of the same biological pathway(s) [1]. Previous studies have demonstrated that miRs are dysregulated and functionally involved
in rheumatoid arthritis (RA) [2-9]. In this study we sought to identify novel miR associations in synovial fibroblasts
(SFs), a key pathogenic cell type in RA [10,11], by performing miR expression profiling on cells isolated from the human TNF transgenic
mouse model (TghuTNF, Tg197) [12] and patients biopsies.

Materials and methods

miR expression in SFs from TghuTNF and WT control mice were determined by deep sequencing
and the arthritic profile was established by pairwise comparisons. qRT-PCR analysis
was utilised for profile validation, miR and gene quantitation in patient SFs. Dysregulated
miR target genes and pathways were predicted via bioinformatic algorithms.

Results

Deep sequencing demonstrated that TghuTNF-SFs exhibit a distinct pathogenic profile
with 22 significantly upregulated and 30 significantly downregulated miRs (fold change>1.5,
p-value<0.05). qRT-PCR validation assays confirmed the dysregulation of miR-223, miR-146a
and miR-155 previously associated with human RA pathology, as well as that of miR-221/222
and miR-323-3p. Notably, the latter were also found significantly upregulated in patient
RASFs, suggesting their association with human RA pathology. Bioinformatic analysis
suggested Wnt/Cadherin signaling as the most significant pathway targets of miR-221/222
and miR-323-3p and CSNK1A1 and BTRC, the negative regulators of β-catenin, amongst
predicted gene targets. qRT-PCR assays confirmed the downregulation of these genes
in RASFs, validating our hypothesis that the newly identified miRs may function to
modulate Wnt/Cadherin signaling.

Conclusions

In this study, by performing comparative analyses between an established mouse model
of arthritis and RA patient biopsies, we identified novel dysregulated miRs in RASFs
potentially involved in pathways important for the pathogenic phenotype of these cells
and highlighting the value of such cross-species comparative approaches [13].

Acknowledgements

This project was funded by the Masterswitch Project (HEALTH-F2-2008-223404), EURO-RA
RTN (HPRN-CT-2002-00255) and IMI BtCure (grant agreement No 115142) grants to GK and
SG. JR was supported by the Wellcome Trust grant 075491/Z/04. In SG also received
funding from IAR-EPALINGES.